A stent is a medical device including a mesh-like cylindrical body in which multiple annular bodies configured to include waved struts having a bending portion are arranged in an axial direction so that the adjacent annular bodies are integrated with each other via a link portion. For example, the stent is applied in order to prevent a restenosis after percutaneous transluminal coronary angioplasty (PTCA) or percutaneous coronary intervention (PCI) which is used in treating myocardial infarction or angina pectoris.
In a case where a so-called bare metal stent which is not coated with a drug is applied, a restenosis rate can be lower than that in a case of the PTCA or the PCI without using the stent at all. However, it has been recognized that restenosis occurs in a stent indwelling portion at a rate of approximately 20% to 30%. A major factor of restenosis is intimal hypertrophy caused by the migration and proliferation of vascular smooth muscle cells. Therefore, drug eluting stents (DES) have been developed which help prevent the restenosis by coating an outer surface of the stent with a drug for inhibiting the migration and proliferation of vascular smooth muscle cells and by eluting the drug in a stent indwelling portion.
For example, as disclosed in JP-T-2011-502723, the drug coating is performed in such a way that a coating solution prepared by dissolving the drug and a biocompatible polymer into a solvent is discharged along an outer surface of a strut by using a spray nozzle, and thereafter, is dried and solidified.
In general, the stent is expanded and deformed when the stent indwells after reaching a target portion inside a lumen. Therefore, due to the expanding deformation, stress concentration and/or distortion occurs in a drug coating layer formed on an outer surface of a bending portion of the strut. Consequently, there is a problem in that the drug coating layer is peeled off or separated therefrom.
In order to solve this problem, a stent disclosed in pamphlet of International Publication No. 2011/040218 employs a bending portion serving as a non-coating layer which is not coated with a drug, thereby preventing a coating layer from being peeled off and separated. In addition, as a method of forming the non-coating layer, when a nozzle for discharging the drug reaches the bending portion, the nozzle is caused to perform separating movement (jumping) from the bending portion, thereby preventing the bending portion from being coated with the drug.
In a case where the above-described method is employed, although the bending portion can be suitably prevented from being coated with the drug, the nozzle inevitably stores the drug while the nozzle performs the separating movement. Consequently, the drug is excessively discharged immediately after the nozzle passes through the bending portion. For example, in some cases, not only an outer surface which is initially supposed to be coated but also a side surface portion is coated with the drug. Consequently, there is a possibility that the drug may no longer be uniformly effective, or that poor yields may be expected when the stent is manufactured.